The present disclosure relates generally to the field of analog to digital conversion and more specifically to photonic analog to digital signal conversion.
Conventional military RF systems conventionally include wide bandwidth, high resolution Analog-to-Digital Converters (ADC) to enable use of, for example, wideband staring Signals Intelligence (SIGINT) receivers, flexible Software Defined Radio system architectures, and Lower Probability of Intercept/Lower Probability of Detection (LPI/LPD) radars. Conventional electronic ADC (eADC) performance may significantly limit the potential of such systems.
Optical or photonic ADCs (pADCs) were originally intended to advance the state of the art in analog to digital conversion, however conventional photonic ADC approaches have not been practical due to limitations such as size, weight, power consumption, poor Spurious-Free Dynamic Range (SFDR), fractions of continuous time, etc., making traditional eADCs more attractive and practical.
One conventional attempt at developing a pADC uses a mode locked laser to optically sample an RF signal that is applied to a parallel array of varying length mach-zehnder interferometers. Each interferometer is followed by a one bit electronic ADC to generate a digital code. Another conventional pADC approach uses temporal demultiplexing to reduce the sampling rate to a rate that electronic ADCs can digitize. Various conventional pADCs may achieve performances of about 10 ENOB at 505 MS/s, 3 ENOB @ 50 GHz as a transient digitizer at 10 TS/s of a 90 GHz waveform, 7 ENOB @ 10 GHz in a 2 channel system, and 3 ENOB @ 10 GHz at 150 GS/s with 4 channels. However, none of the pADC implementations to date have demonstrated practical chip-scale pADCs that can be used in the field.
Conventional electronic ADCs are a choke point in achieving multi-Gigabit rates in military and commercial receivers. The lack of availability of high-precision, high-speed ADCs limits the performance and has driven the complexity of receivers. The low-precision of conventional high-speed ADCs limits the dynamic range of the receiver.
What is needed is an ADC capable of simultaneously achieving high-dynamic range with high-data rates, allowing the receiver to capture and process high volumes of data in a highly dynamic spectral environment. What is also needed is a pADC having more practical size, weight, power consumption, SFDR, fractions of continuous time, etc. What is also needed is a more practical pADC having performance greater than that of eADCs. What is further needed is a pADC that is not inhibited by the clock jitter limitations of eADCs. What is still further needed is a pADC that can be used in RF communications systems.